Sleep apnoea is a major hazard in people of all ages and much innovative thinking has gone to develop various techniques for detecting the occurrence of apnoea. Many complex proposals have been made in efforts to provide suitable equipment. One example is described in EP 0484174, relies on battery power, on contacts and on other components that are subject to failure. Also, the possibility of using the piezoelectric and pyroelectric properties of PVDF (poly vinylidene flouride) films for developing transducers to sense the presence or absence of breathing, is described in U.S. Pat. No. 5,311,875 which uses the PVDF film to sense the temperature differences between the inspired and expired breaths, and WO 97/05824. It is not known, however, whether any proposals have progressed beyond theory or experimentation.
Respiratory rate is one of the most important physiological parameters. It is a component of most medical and nursing records and is used in many clinical scoring systems. Extremes of respiratory rate indicate the need for urgent intervention. Even today, in the case of non-intubated patients, the measurement of respiration rate is based on human observation alone, although this is known to be highly inaccurate.
Pyroelectric sensitive transducers incorporated in a face mask can be used to provide a quantitative measure of the respiratory rate in an easy and affordable manner. Furthermore, suitable circuitry for a respiratory monitor incorporating a PVDF sensor is described in our co-pending Patent Application GB 0201095.7.
As breathing could be wholly nasal, wholly oral, or part nasal and part oral, with changes between the modes, particularly during sleep, a problem for all workers in the field is optimum creation of a transducer to ensure that the patients' breath, if breathing, will always impinge upon the transducer, so obviating any false reading.